The present invention relates generally to nuclear steam generators, and in particular to a new and useful tube support system and method for use in nuclear steam generators which employ tube support plates to retain the tube array spacing within the steam generator.
The pressurized steam generators, or heat exchangers, associated with nuclear power stations transfer the reactor-produced heat from the primary coolant to the secondary coolant, which in turn drives the plant turbines. These steam generators may be as long as 75 feet and have an outside diameter of about 12 feet. Within one of these steam generators, straight tubes, through which the primary coolant flows, may be ⅝ inch in outside diameter, but have an effective length of as long as 52 feet between the tube-end mountings and the opposing faces of the tube sheets. Typically, there may be a bundle of more than 15,000 tubes in one of these steam generators. It is clear that there is a need to provide structural support for these tubes, such as a tube support plate, in the span between the tube sheets to ensure tube separation, adequate rigidity, and the like.
U.S. Pat. No. 4,503,903 describes apparatus and a method for providing radial support of a tube support plate within a heat exchanger, such as a U-tube steam generator having an inner shell and an outer shell. The apparatus is rigidly attached to the inner shell, and is used to centrally locate the tube support plate within the inner shell.
U.S. Pat. No. 5,497,827 describes apparatus and method for radially holding a tube support within a U-tube steam generator. Abutments radially separate an inner bundle envelope, or inner shell, from an outer pressure envelope. Each abutment is fixed to the inner bundle envelope by welding, and contacts the inner face of the pressure envelope. The abutments maintain the different coaxial envelopes of the steam generator and the assembly of the bundle by spacer plates in the radial directions. This is done to avoid relative displacements and shocks between the envelopes and the bundle in the case of external stresses, such as those accompanying an earthquake. In one variant, elastic pressure used to make contact with a spacer plate is obtained by a spiral spring. The spring is located internal to the pressure envelope.
U.S. Pat. No. 4,204,305 describes a nuclear steam generator commonly referred to as a Once Through Steam Generator (OTSG), the text of which is hereby incorporated by reference as though fully set forth herein. An OTSG contains a tube bundle consisting of straight tubes. The tubes are laterally supported at several points along their lengths by tube support plates. The tubes pass through tube support plate holes having three bights or flow passages, and also having three tube contact surfaces for the purpose of laterally supporting the tubes. It is generally recognized that after a heat exchanger is assembled, the tubes will contact one or two of the inwardly protruding lands of the tube support plate holes. This contact provides lateral support to the tube bundle to sustain lateral forces such as seismic loads, as well as provides support to mitigate tube vibration during normal operation.
U.S. Pat. No. 6,914,955 B2 describes a tube support plate suitable for use in the aforementioned OTSG.
For a general description of the characteristics of nuclear steam generators, the reader is referred to Chapter 48 of Steam/Its Generation and Use, 41st Edition, The Babcock & Wilcox Company, Barberton, Ohio, U.S.A., © 2005, the text of which is hereby incorporated by reference as though fully set forth herein.